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51.
Guilherme T. de Assis Alberto H. F. Laender Marcos André Gonçalves Altigran S. da Silva 《World Wide Web》2009,12(3):285-319
Focused crawlers have as their main goal to crawl Web pages that are relevant to a specific topic or user interest, playing
an important role for a great variety of applications. In general, they work by trying to find and crawl all kinds of pages
deemed as related to an implicitly declared topic. However, users are often not simply interested in any document about a
topic, but instead they may want only documents of a given type or genre on that topic to be retrieved. In this article, we
describe an approach to focused crawling that exploits not only content-related information but also genre information present
in Web pages to guide the crawling process. This approach has been designed to address situations in which the specific topic
of interest can be expressed by specifying two sets of terms, the first describing genre aspects of the desired pages and
the second related to the subject or content of these pages, thus requiring no training or any kind of preprocessing. The
effectiveness, efficiency and scalability of the proposed approach are demonstrated by a set of experiments involving the
crawling of pages related to syllabi of computer science courses, job offers in the computer science field and sale offers
of computer equipments. These experiments show that focused crawlers constructed according to our genre-aware approach achieve
levels of F1 superior to 88%, requiring the analysis of no more than 65% of the visited pages in order to find 90% of the
relevant pages. In addition, we experimentally analyze the impact of term selection on our approach and evaluate a proposed
strategy for semi-automatic generation of such terms. This analysis shows that a small set of terms selected by an expert
or a set of terms specified by a typical user familiar with the topic is usually enough to produce good results and that such
a semi-automatic strategy is very effective in supporting the task of selecting the sets of terms required to guide a crawling
process. 相似文献
52.
Degree-Optimal Routing for P2P Systems 总被引:1,自引:0,他引:1
Giovanni Chiola Gennaro Cordasco Luisa Gargano Mikael Hammar Alberto Negro Vittorio Scarano 《Theory of Computing Systems》2009,45(1):43-63
We define a family of Distributed Hash Table systems whose aim is to combine the routing efficiency of randomized networks—e.g.
optimal average path length O(log 2
n/δlog δ) with δ degree—with the programmability and startup efficiency of a uniform overlay—that is, a deterministic system in which the overlay network is transitive and greedy routing is optimal. It is known that Ω(log n) is a lower bound on the average path length for uniform overlays with O(log n) degree (Xu et al., IEEE J. Sel. Areas Commun. 22(1), 151–163, 2004).
Our work is inspired by neighbor-of-neighbor (NoN) routing, a recently introduced variation of greedy routing that allows us to achieve optimal average path length in randomized networks. The advantage of our proposal is that of allowing
the NoN technique to be implemented without adding any overhead to the corresponding deterministic network.
We propose a family of networks parameterized with a positive integer c which measures the amount of randomness that is used. By varying the value c, the system goes from the deterministic case (c=1) to an “almost uniform” system. Increasing c to relatively low values allows for routing with asymptotically optimal average path length while retaining most of the advantages
of a uniform system, such as easy programmability and quick bootstrap of the nodes entering the system.
We also provide a matching lower bound for the average path length of the routing schemes for any c.
This work was partially supported by the Italian FIRB project “WEB-MINDS” (Wide-scalE, Broadband MIddleware for Network Distributed
Services), . 相似文献
53.
月球探测(车)机器人技术的发展与展望 总被引:1,自引:0,他引:1
简述当前国内外探月研究进展及月球探测(车)机器人研究发展情况.基于月球的复杂环境特征,对比轮式运动与步行式运动月球探测(车)机器人的优势与缺陷,重点介绍了一种新型六轮腿式月球探测机器人方案.该方案具有高机动性,越障能力强,容错性好等特点,对该方案主要技术性能、本体结构、运动系统、轮腿切换机构工作原理等关键技术进行了探讨. 相似文献
54.
Applied Intelligence - Forecasting future heat load in smart district heating networks is a key problem for utility companies that need such predictions for optimizing their operational activities.... 相似文献
55.
A growing number of patients are recognised to have chronic kidney disease (CKD). However, only a minority will progress to end-stage renal disease requiring dialysis or transplantation. Currently available diagnostic and staging tools frequently fail to identify those at higher risk of progression or death. Furthermore within specific disease entities there are shortcomings in the prediction of the need for therapeutic interventions or the response to different forms of therapy. Kidney and urine proteomic biomarkers are considered as promising diagnostic tools to predict CKD progression early in diabetic nephropathy, facilitating timely and selective intervention that may reduce the related health-care expenditures. However, independent groups have not validated these findings and the technique is not currently available for routine clinical care. Furthermore, there are gaps in our understanding of predictors of progression or need for therapy in non-diabetic CKD. Presumably, a combination of tissue and urine biomarkers will be more informative than individual markers. This review identifies clinical questions in need of an answer, summarises current information on proteomic biomarkers and CKD, and describes the European Kidney and Urine Proteomics initiative that has been launched to carry out a clinical study aimed at identifying urinary proteomic biomarkers distinguishing between fast and slow progressors among patients with biopsy-proven primary glomerulopathies. 相似文献
56.
When performing a classification task, we may find some data-sets with a different class distribution among their patterns. This problem is known as classification with imbalanced data-sets and it appears in many real application areas. For this reason, it has recently become a relevant topic in the area of Machine Learning.The aim of this work is to improve the behaviour of fuzzy rule based classification systems (FRBCSs) in the framework of imbalanced data-sets by means of a tuning step. Specifically, we adapt the 2-tuples based genetic tuning approach to classification problems showing the good synergy between this method and some FRBCSs.Our empirical results show that the 2-tuples based genetic tuning increases the performance of FRBCSs in all types of imbalanced data. Furthermore, when the initial Rule Base, built by a fuzzy rule learning methodology, obtains a good behaviour in terms of accuracy, we achieve a higher improvement in performance for the whole model when applying the genetic 2-tuples post-processing step. This enhancement is also obtained in the case of cooperation with a preprocessing stage, proving the necessity of rebalancing the training set before the learning phase when dealing with imbalanced data. 相似文献
57.
Alberto Pardo Jo?o Paulo Fernandes Jo?o Saraiva 《Higher-Order and Symbolic Computation》2011,24(1-2):115-149
Functional programs often combine separate parts using intermediate data structures for communicating results. Programs so defined are modular, easier to understand and maintain, but suffer from inefficiencies due to the generation of those gluing data structures. To eliminate such redundant data structures, some program transformation techniques have been proposed. One such technique is shortcut fusion, and has been studied in the context of both pure and monadic functional programs. In this paper, we study several shortcut fusion extensions, so that, alternatively, circular or higher-order programs are derived. These extensions are also provided for effect-free programs and monadic ones. Our work results in a set of generic calculation rules, that are widely applicable, and whose correctness is formally established. 相似文献
58.
Antonio Fernández Anta José Luis López-Presa M. Araceli Lorenzo Pilar Manzano Juan Martinez-Romo Alberto Mozo Christopher Thraves 《Theory of Computing Systems》2011,48(1):1-22
In this paper we generalize the Continuous Adversarial Queuing Theory (CAQT) model (Blesa et al. in MFCS, Lecture Notes in
Computer Science, vol. 3618, pp. 144–155, 2005) by considering the possibility that the router clocks in the network are not synchronized. We name the new model Non Synchronized
CAQT (NSCAQT). Clearly, this new extension to the model only affects those scheduling policies that use some form of timing.
In a first approach we consider the case in which although not synchronized, all clocks run at the same speed, maintaining
constant differences. In this case we show that all universally stable policies in CAQT that use the injection time and the
remaining path to schedule packets remain universally stable. These policies include, for instance, Shortest in System (SIS)
and Longest in System (LIS). Then, we study the case in which clock differences can vary over time, but the maximum difference
is bounded. In this model we show the universal stability of two families of policies related to SIS and LIS respectively
(the priority of a packet in these policies depends on the arrival time and a function of the path traversed). The bounds
we obtain in this case depend on the maximum difference between clocks. This is a necessary requirement, since we also show
that LIS is not universally stable in systems without bounded clock difference. We then present a new policy that we call
Longest in Queues (LIQ), which gives priority to the packet that has been waiting the longest in edge queues. This policy
is universally stable and, if clocks maintain constant differences, the bounds we prove do not depend on them. To finish,
we provide with simulation results that compare the behavior of some of these policies in a network with stochastic injection
of packets. 相似文献
59.
60.
Julio Vera Carlos González-Alcón Alberto Marín-Sanguino Néstor Torres 《Computers & Operations Research》2010,37(8):1427-1438
In this work we present a general (mono and multiobjective) optimization framework for the technological improvement of biochemical systems. The starting point of the method is a mathematical model in ordinary differential equations (ODEs) of the investigated system, based on qualitative biological knowledge and quantitative experimental data. In the method we take advantage of the special structural features of a family of ODEs called power-law models to reduce the computational complexity of the optimization program. In this way, the genetic manipulation of a biochemical system to meet a certain biotechnological goal can be expressed as an optimization program with some desired properties such as linearity or convexity.The general method of optimization is presented and discussed in its linear and geometric programming versions. We furthermore illustrate the use of the method by several real case studies. We conclude that the technological improvement of microorganisms can be afforded using the combination of mathematical modelling and optimization. The systematic nature of this approach facilitates the redesign of biochemical systems and makes this a predictive exercise rather than a trial-and-error procedure. 相似文献